Engine Misfire and hesitation

I have seen this problem before it happens when the shop installs the wrong weight oil and it pumps up the lifters and stops compression causing the engine to stall. Here is a guide to help you change the oil out for the correct weight oil.

https://www.2carpros.com/articles/how-to-change-engine-oil-and-filter

Please run down this guide and report back.

Thank you..I changed the oil to this after I found this info

1.GM6094M Your vehicle's engine requires oil meeting GM Standard GM6094M.

2.SAE 5W-30 is best for your vehicle. These numbers on an oil container show its viscosity, or thickness. Do not use other viscosity oils such as SAE 20W-50. Oils meeting these requirements should also have the starburst symbol on the container. This symbol indicates that the oil has been certified by the American Petroleum Institute (API). You should look for this information on the oil container, and use only those oils that are identified as meeting GM Standard GM6094M and have the starburst symbol on the front of the oil container.

NOTICE: Use only engine oil identified as meeting GM Standard GM6094M and showing the American Petroleum Institute Certified For Gasoline Engines starburst symbol. Failure to use the recommended oil can result in engine damage not covered by your warranty.

GM Goodwrench oil meets all the requirements for your vehicle.

If you are in an area of extreme cold, where the temperature falls below -20°F (-29°C), it is recommended that you use either an SAE 5W-30 synthetic oil or an SAE 0W-30 oil. Both will provide easier cold starting and better protection for your engine at extremely low temperatures.

ENGINE OIL ADDITIVES

Do not add anything to your oil. The recommended oils with the starburst symbol that meet GM Standard GM6094M are all you will need for good performance and engine protection.
Capacities


Engine Oil with Filter .................... 4.0 quarts (3.8 liters)

NOTE: All capacities are approximate. When adding, be sure to fill to the approximate level. Recheck fluid level after filling.

The car has issues picking up speed from a stop, going up hills I will loose anywhere from
5-20mph unless I make the tranny downshift, the car will rev up just fine if you hit the gas good enough, but when I'm cruising it doesn't want to go above 2grand without a healthy downshift.

Tests-
Vacuum- at idle it fluctuated +/- 1 at 17"hg
1000rpm-18-19
2500rpm-20-21
Snap throttle- down to zero and up to 25"hg then very gradually returns to 17"hg fluctuating +/-1

Compression
1- 203psi
2- 195psi
3-205psi
4-201psi
5-198psi
6- 201psi

Tried-inatke manifold gasket upper and lower
Spark plugs (gapped right on .040)
Wires
Air filter
Tried swapping coils
Cleaning throttle body (needed it)
Fuel trim reset (after replacing any of the above)
Cam sensor
Maf cleaned

The issue- no CEL, no missfire (idle,cruising,heavy load)
Idles smooth but when I come to a stop it goes from 750-800 to about 575-600 when I'm holding the brake in drive. Rpms jump (only when I'm cruising and I let off the gas) tranny shifts fine, exhaust note is irregular (sounds rough) car gets ok gas mileage if I don't make it downshift too much, getting on the onramp at the beginning it feels as I'f I have a complete hesitation and no acceleration until I tap the gas a little more then it continues as.usual.

Helpful information- when I.did the intake I.noticed one Pushrod was. Stressed more so then the other 11 and it was very very very slightly bent, I don't know if this has anything to do with it tho since compression was good. I do also have a little more valve train noise as apossed to normal operation. Idle sounds a little weird to with a constant lope sound/feel (very little if any rpm change(25-50rpm)

Let me clarify the vacuum only fluctuated +/- 1 at idle
1000rpm- 19
2500rpm- 21

Vac gauge to fluctuate like that could be just the valve over lap where both valves are open-could also be an exhaust restriction/also check the throttle position sensor/EGR valve

Ok and could one slightly bent pusrod cause this? And what would be a definitive test to rule out the tps? I'll pull the pre cat 02 later and see if it helps.

A bent pushrod will affect the valve lash clearance and cause the valve not to open/close properly on time-You check the TPS closed and wide open throttle voltages

My car blew a head gasket and my shop removed head and had them checked and resurfaced and now Car Misfires at steady cruising speed, but doesn't do it at idle or exceleration. Replace plugs and wires,coil,ecm, crank sensor, checked wire harness for injectors and still no help. Also had trans checked and it's ok. Any suggestions? Allan

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel

I have an ongoing mild engine miss when idling. I have already replace the fuel filter, spark plugs, wires and added a gas additive. I have also checked for arcing at night on the wires, but haven't been able to find any problems there. The car worked fine until I recently had the transmission overhauled. Could there be something that they may have done to create this problem. The service engine light has not come on or any other codes. Is there something else that may be causing this miss in the engine. Please let me know what you think.
Thanks
Brian

Hi Brian:

Since there are no codes, and the problem started after the trans repairs, I would look for a vacuum problem. They may have left a hose off or damaged one without realizing.

Let me know if this helps, or if you have any other questions.

Joe

Thanks Joe for replying.

I have had a look to see if any vacuum lines were off or pinched shortly after this started and didn't really see anything. I will go overthem again, I might have missed something and let you know.

Thanks
Brian

Hi Joe,

I just went over the car again and couldn't see any lines that were lose, kinked or off. Look like we are back to square one. Someone else mentioned putting Berryman's B-12 cleaner in it for the injectors. Their thought is possibly fuel. I have already put in injector cleaner and changed the fuel filter. Do you think that this would help or a waste of money?